She told an internal audit conference in Johannesburg that her presence was part of her mandate, and was aimed at gaining and maintaining confidence from concerned parties.
"I must indicate that we do not arbitrarily adapt our operations because one stakeholder or group wants things done their way," she said.
"Mine is always a principled decision that can stand the test of the standards set in the Constitution, particularly the requirements of independence, impartiality, and operating without fear or favour."
ANC chief whip Mathole Motshekga has called Madonsela's decision to attend the Women's Day event in Port Elizabeth "ill-considered".
Motshekga said the public protector had "rubbed shoulders" with DA leaders at the event. He argued that Madonsela was jeopardising her constitutional role of independence and impartiality.
"Attending and giving keynote addresses at political events of political parties has the potential to compromise these basic constitutional principles," Motshekga said.
The South African Communist Party also weighed in on the criticism, and said Madonsela's attendance had compromised her office.
However, Madonsela said her attendance was a principled move, as she travelled across the country as part of the public protector's annual stakeholder consultative dialogue, which began in July.
The 2012 dialogue incorporated public hearings on ongoing investigations, and interest groups, including political parties, had meetings lined up with her.
"Meetings are scheduled to take place with political parties at the end of the process. Incidentally, the ANC is, as was the case last year, getting its own meeting while the opposition parties get a combined meeting," said Madonsela.
"The meeting that has incurred the ire of a chief whip of one of the political parties in Parliament and an organisation affiliated to this party belongs to this category of meetings." – Sapa